Start a fresh Seamonkey (no cookies, empty cache).
Open only one web site. For example : news.com.au
Open in another tab : about:cache?device=memory
You will see many entries : note which are for advertisements.

Open /etc/hosts as text with geany.
Add the advertisements to be blocked.
For instance add the lines :
0.0.0.0 pagead2.googlesyndication.com
0.0.0.0 partner.googleadservices.com
0.0.0.0 googleads.g.doubleclick.net
Etc. Etc.
There can be dozens of them.
Save.

Leave Seamonkey and reopen the example website.
You will see it loading cleaner and faster.
Do this for all your favorite websites.Edited_time_total

Nice tips linuxcbon.
It can however be applied to pretty much any browser and O.S.

I generally detest adverts when browsing for two reasons:

1) Wastes my time
2) Wastes my bandwidth/cap.

I do make one or two exceptions and one being the advert shown on this forum.
It takes money to maintain and host a site like this one and since it helps me,
I don't block ads here.

Once you know which ads you want to block, simply edit your hosts file
and presto, no more annoying adverts.

The location of your hosts file will differ depending on your O.S.
A few examples:

For NT, Win2K & XP, it's located in "C:\windows\system32\drivers\etc\hosts"
or "C:\winnt\system32\drivers\etc\hosts"

For Windows 7 & Vista, it's in "C:\windows\system32\drivers\etc\hosts"
or "%systemroot%\system32\drivers\etc\hosts"

Keep in mind that if you have anti-virus software running (M$ Security Essentials included),
you will have to either temporarily disable the anti-virus software or allow the change.

For Linux, simply search for /etc/hosts
Remember that for non-root distros such as Ubuntu, you will first have to run as root.

For Mac, I have no idea.

When editing the hosts file, always use the top level domain name
such as:

0.0.0.0 www.google-analytics.com

and not:

0.0.0.0 http://www.google-analytics.com/ga.js

Depending on your setup, you may also have to replace 0.0.0.0 with 127.0.0.1

Of course this method is not limited to blocking just adverts and can be
used to protect other members of your household from "nasty" sites.
There are plenty of lists on the net for all sorts of unsavoury websites
which you can add to your hosts file.

If you use Yahoo and don't want all the pics and flash ads all over the place,
add the following entries to your hosts file:

0.0.0.0 l1.yimg.com
0.0.0.0 l.yimg.com
0.0.0.0 row.bc.yahoo.com

You may have to add a few more that Yahoo uses for it's localisation
depending on which country you're in.
It now loads in a quarter of the time, admittedly it does not look as pretty but
saves a lot of bandwidth by not loading all that "eye-candy".